Continuous type furnace



arch 4, i952 J. l.. MGFARLAND ET AL 2,588,141

CONTINUOUS TYPE FURNACE Filed Sept. 22, 1948 Inventor: M

James L3. McFarland NOT-ma B.Jovwes Their Att Orr/1 ey.

Patented Mar. 4, 1952 CONTINUOUS TYPE FURNACE James L. McFarland, Schenectady, and Norman B. Jones, Ballston Lake, N. Y., assignors to General Electric Company, a corporation of New York Application September 22, 1948, Serial No. 50,506

2 Claims. 1

Our invention relates to furnaces, particularly to high temperature furnaces of the type adapted for continuous operation including roller hearth furnaces and the chain conveyor type. Our invention has for its object to provide an improved furnace and furnace conveying system which furnishes uniform heating and economical operation with a reasonable first cost.

Heretofore, roller hearth furnaces have been limited to a practical width of a few feet, when used for high temperature Work, because of the adverse effect of high temperatures on the physical strength of the rolls. Accordingly, it is a further object of our invention to provide roller hearth type furnaces of much greater width than present designs permit.

Again, conventional chain conveyor furnaces do not provide uniform heating when used at high temperatures because of the necessity for keeping the conveyor chain cooler than the furnace proper and because of the escape of heat through necessary openings in the furnace insulation. It is therefore another object of our invention to provide a chain conveyor type furnace, especially one of large physical size, which can be operated at high temperatures with uniform results.

In carrying out our invention in one form we provide a continuous roller hearth type electric furnace with two parallel rows of rollers extending the full length of the furnace. These rollers support suitable elevated carrying devices which, in turn, support the work to be heated. The rollers are recessed in the floor ofthe furnace, and the recesses are completely insulated so that there is no large heat loss. While these recesses are maintained at practically full furnace temperature, the rollers are comparatively short and, therefore, can be designed to withstand high temperatures without exceeding the stress limitations of the metal of which they are made. 'I'he rollers are driven in synchronism by a suitable external means.

For a more complete understanding of our invention, reference should be had to the attached drawing which shows in Fig. 1 a side view of one form of our invention; Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1; and Fig. 3 is a partial detailed sectional View taken along the line 3-3 of Fig. 2.

Referring to Fig. 1 of the drawing, the rollers l can be seen extending thev full length of the furnace; Fig. 2 shows the relation of the rollers to the insulated recesses 2 in the furnace floor. The rollers l support the elevated carrying devices or fixtures 3 which, in turn, support the 1 example, to approximately 1000 F. In zone 2,

Work pieces 4 to be heated. The rollers I are 'Y driven in synchronism by a suitable driving means such as electric motor 5, best seen in Fig. 2,

through a suitable driving mechanism such as continuous chain 6 and sprockets 1, which Aare pling assembly 8 so that the left row of rollers in "Fig. 2 is driven from and in synchronism with the right row which, in turn, is driven by the motor and chain and sprocket mechanism.

In the operation of this furnace, the elevated lcarriers or fixtures 3 supporting the Work to be heated 4 are brought to the furnace by a suitable conveyor 9. The door IU is opened to admit the supporting xtures and work to the furnace and they pass through the furnace from left to right in Fig. 1. In zone l, the work is preheated, *for the final heating takes'place and the temperature of the work is raised, for example, to approximately 1725 F. In zone 3 of the furnace, the work is cooled, for example, to approximately 1200 F. Door H is then opened and the work and the supporting fixtures are discharged onto a suitable conveyor 2 which removes them from the furnace. The work can be allowed to cool naturally after it has been removed from the furnace or it can be cooled more rapidly by an air blast or ,other suitable means (not shown) as it is being removed from the furnace.

This furnace is heated electrically by electric heaters I3 distributed throughout the furnace.-

However, our invention is equally applicable to furnaces heated by other conventional means, such as natural or manufactured gas or oil.

Furthermore, While our improved furnace has been illustrated as employing two complete sets orv rows of rollers, any desired numberv of such sets or rows may be employed. Bytheuse of a suitable number of rows of rollers, furnaces can be made any desired width by the use of our nvention. Heretofore, roller hearth furnaces have been limited to a width of approximately 81/2 feet when constructed for operation at 1650D F. because of the adverse effect of such a high temperature on the physical strength of the rolls, this width being the over-all outside dimension; the corresponding inside Wall to wall width in the heating chamber is approximately 6 feet. At 2050 F., the present practical maximum outside width is approximately 5 feet, which gives an inside Working width of approximately 30 inches.

One modification of our invention relates to the use of rollers. similar to those already .described, in completely insulated recesses in the floor of the furnace to support one or more chain conveyors. These chain conveyors are conventional in form except that they are made of special alloy steel to withstand full furnace temperature. They have dogs or other prolecting members on them which project above the furnace floor and propel the work to be heated along the floor of the furnace from the entrance to the exit. This arrangement is applicable primarily to large pipes and other similar objects which will roll tlirough the furnace when pushed by the dogs on the conveyor chains. Alternatively, if the material to be heated is not suitable for rolling, the conveyor chains can be made of such dimensions that they support the weight of the work 1n the furnace While they, in turn, are supported by the recessed rollers. y

Tile use oi sucli a cilaiii conveyor or conveyors operating at ruil furnace temperature is made practical oy the use ol the recessed supporting rollers of our invention. These rollers greatly reduce the il'lctloil oil tile chalii or ciiallls wl'ilcll, in turll, ieduces trie size ol chains required to witilin practical limits lor the special alloy steel wllich is required to withstand nign temperatures. Conventional chain conveyor type iurnaces, where the chains are supported in metal guides somewhat below the 1100i` oi the furnace, are not practical for use at high temperatures in large installations. The chains must be of special` alloy steel to withstand the temperature, and the large friction load, caused by tile weight or tile chains themselves in the metal guides, in addition to the work being propelled through the furnace, makes the chains so large that the cost is prohibitive.

Furthermore, on conventional chain conveyor furnaces there usually are slots cut in the floor insulation t permit the dogs on the conveyor chains to prolect through the floor and engage the work-piece. These slotspermit the escape ofv large amounts of heat from the furnace which lowers its efficiency and at the same time cause cold spots in the work. Our invention, utilizing completely insulated recesses in the furnace floor, prevents the escape of large quantities of heat from the furnace and causes the work to be heated uniformly.

When our invention is applied to a chain conveyor furnace, it is n'ot necessary for the rollers to be independentlydriven from an external source, as shown on the accompanying drawing and described above for the roller hearth arrangement. In this modification, the conveyor chain or chains are driven by a suitable external means, such as an electric motor, and the rollers are used` merely to support the chains.

It is generally knownthat high temperature electric furnaces are, very often equipped with l means for providing an artificial non-oxidizing reducing atmosphere utilizing such gases as hydrogen, or a mixture of hydrogen and nitrogen, or atmosphere convertor gas which is made by burning suitable manufactured or natural gas with a controlled deficiency of air. Hign temperature furnaces are sometimes used without artificial atmosphei'e, however, for some kinds of material. Our invention is suitable for application to furnaces with or without artificial atmosphere.

While we have described one preferred embodiment'of our invention along with one modification, many other modifications will occur to those skilled in the art and it should, therefore, be understood that we intend by the appended claims'to cover alll such modifications which fall withinthe true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1`. A horizontally disposed furnace of the type adapted for continuous conveyor operation having a plurality of parallel insulated recesses in the oor of the furnace heating chamber and extending longitudinally througii said furnace, a plurality of rollers extending transversely through one of said recesses, an equal number of rollers extending transversely through each of the other recesses, means supported by said rollers for propelling work through the furnace, means external to said heating chamber for connecting together corresponding rollers in separate recesses, and means external to said heating chamber for driving said rollers irl syncnronism to actuate said work propelling means.

2. A horizontally disposed furnace adaptable for continuous conveyor operation having a plurality of parallel insulated recesses in the floor of the furnaceV heating chamber extending longitudinally through said furnace, a plurality of REFERENCES YCITED 'The following references' are'of record in the file of this patent:

UNITED STATES PATENTS l Date Number Name 489,017 Koch Jan. 3, 1893 786,565 Hughes Apr. 4, 1905 1,362,369 Talley ,Dec. 14, 1920 Wean Sept. 29, 1931 

